Antiviral activity of the bicyclic nucleosides such as 5,6-dichloro-1-(.beta.-D-ribofuranosyl) benzimidazole (DRB) and some closely related derivatives has been previously reported. Activity of those compounds against specific viruses, such as the RNA viruses, has also been reported.
Benzimidazole nucleosides are particularly attractive as potential antiviral agents because of their stability toward some major pathways of bioactive purine (bicyclic) nucleoside inactivation, e.g., deamination by adenosine deaminase and glycosidic bond cleavage by purine nucleoside phosphorylases. Unfortunately, benzimidazole nucleosides such as DRB which have been previously described as having antiviral activity also have generally unacceptable levels of cytotoxicity, thereby greatly diminishing their usefulness in the treatment of viral infections in animals. It would thus be very desirable to develop derivatives of these compounds having increased antiviral properties with decreased cytotoxicity.